Titanium components are finding increased importance in both military and commercial applications because of their light weight, excellent mechanical properties, and corrosion resistance. However, conventional manufacturing processes such as investment casting and ram graphite casting result in high cost of near net shape structures. This is due to a combination of factors including material cost, tooling cost, and processing costs including labor costs. In addition castings frequently have defects and voids compromising the mechanical properties of the components. A rapid manufacturing process, also known as solid free form fabrication (SFFF), that uses a laser to melt titanium can deposit 3-dimensional near net shapes, without the need for tooling. However, the capital and operating costs for the laser SFFF process result in component costs substantially higher than either investment or ram graphite casting.
The use of the PTA torch in an SFFF process can produce three dimensional or shaped components at a lower cost than typical Ti alloy manufacturing methods such as investment casting or ram graphite casting. While the PTA-SFFF process can reduce the cost of Ti alloy components compared to available alternatives, conventional PTA-SFFF processes still require the use of relatively expensive titanium alloy wire or powder feeds. Thus, a further cost reduction would be desirable to enable the use of Ti alloys in a broader range of applications. An analysis of the costs of near net shape components produced by the PTA-SFFF process reveals that the single largest cost factor is the cost of the titanium feed which may be powder or wire. The lowest cost form in which Ti can be purchased is in the primary sponge form. However, commercially available Ti sponge does not contain any alloying elements and thus cannot advantageously be used in an SFFF process to produce high strength alloys. Thus, typically either prealloyed powder or prealloyed welding wire is used as feed for the SFFF process. However, the cost of alloyed powders is higher than the cost of welding wire, so the use of wire generally is preferred for a lower cost SFFF process. The cost of pure Ti wire (CP Ti) is lower than that of alloyed Ti wire and one potential route for a cost reduction is to utilize the CP Ti wire with the alloying elements as co-feeds to produce alloys. In fact, there is considerable prior art describing the manufacture of Ti welding wire which contains powders of the desired alloying elements. For example, U.S. Pat. No. 2,785,285 describes filling an elongated circumferentially closed sheath of titanium with the desired alloying powders. Another prior art patent describes a Ti tube filled with compacted alloying powders. However, in all the examples cited, the use of a preformed metal sheath is required. This is a costly process, and while these processes can produce alloyed Ti shapes when used in an SFFF process, there is no economic advantage resulting due to materials costs. U.S. Pat. No. 6,680,456 describes the use of a traditionally formed wire feed for PTA SFFF manufacture of metals including Ti. However, this patented process also suffers from high materials costs.